From German Pat. No. 2,909,763 and the corresponding U.S. Pat. No. 4,287,375, it is known to dehydrogenate ethyl benzene by passing a mixture thereof with steam into contact with a catalyst in a tube reactor indirectly heated by molten salts. This process is carried out at a pressure of 0.3 to 1 bar, at a temperature of 580.degree. to 660.degree. C. of the molten salts, a temperature which is not more than 20.degree. C. above the reaction temperature at the catalyst. The steam and ethyl benzene are supplied to the tubes of the reactor in a weight ratio of 1.2 to 1.5.
While this process has proved to be successful, modern energy economics requires minimization of the steam consumption and maximization of the conversion of ethyl benzene to styrene.